1. The Field of the Invention
This invention relates to an X-Y input device, and more particularly to an X-Y input device useful for a graphical display unit.
2. Description of the Prior Art
The graphical display unit is composed essentially of a display screen, a display controller, a data channel and an input device. Various types of input devices are known, and one of them is of "JOISTIC", a registered trade mark. When a lever supported by means of gimbal mechanism is tilted in an intended direction by hand, it detects the derection and tiltangle and then generating voltages or X- and Y-components or the corresponding digital signals. This input device has drawbacks of limited swing range of the lever and unreliable stability of input signals.
To eliminate these drawbacks, recently the so-called mouse has been developed as an input device, which comprises basically a rotatable ball as a steel ball rotatably supported, (which is referred to as "ball" hereinafter), a first roller follower driven by the ball through the utilization of friction between both, a second roller follower driven likewise by the ball through the friction between both, their axes being mutually perpendicular and intersecting, first and second detectors each consisting of a variable resistor and an encoder and adapted to detect rotation quantity of the associated roller follower, and a case holding the ball, first and second roller followers, and first and second detectors for detecting rotation quantity. The term "roller follower" is referred to as "follower" below. The case is provided with an opening through which a lower part of the ball projects downwards. As the ball is caused to roll on a specified flat surface, with hand at the case, towards an intended point, the first and second followers rotates in definite derections. Then directions and rotation quantity of the followers are detected by the first and second detectors as voltages of the X- and Y-components or the corresponding digital signals, which are input to a display unit of the system.